Schottky diode is an important power device and used extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications, such as motor drives, switching of communication device, industry automation and electronic automation and so on. The power devices are usually required characteristics of carrying large forward current, high reverse-biased blocking voltage, such as above 100 volt, and minimizing the reverse-biased leakage current.
A number of power rectifiers have been used to provide high current and reverse blocking characteristics. An exemplary method to form a Schottky barrier diode is disclosed by Chang et al in U.S. Pat. No. 6,404,033. The processes are shown in FIG. 1A to FIG. 1C. Referring to FIG. 1A, a semiconductor substrate having an n+ doped layer 10 and an n−drift layer 12 extended to a first surface 13 is prepared. A field oxide layer 14 is then formed on the first surface 13. Afterward, the field oxide layer 14 is patterned to define positions of guard ring 22 at the termination region. Guard ring regions 22 are then buried into n−drift layer 12 by double implants with B+ and BF2+ as conductive impurities. Thereafter, a thermal anneal process is then performed to drive in and activate the impurities. Thereafter, a second photoresist pattern 24 is then coated on the resultant surface to define an anode region. The results are shown in FIG. 1B.
Referring to FIG. 1C, a wet etch is then performed to remove those exposed field oxide layer 14. After stripping away the photoresist pattern 24, another photoresist pattern 28 having openings is formed on the resultant surface to define trenches at the active region. An etching step is then performed to recess the drift layer 12 using the photoresist pattern 28 as a mask. Another B+ or BF2+ ion implant is then carried out to form p type region 30 buried into trench bottom.
Referring to FIG. 1D, the photoresist pattern 28 is removed. Then, a Schottky barrier metal layer 32 is formed on the resultant surface. Thereafter, a top metal layer formation is followed. A forth photoresist (not shown) and an etch steps are then performed to define the top electrode 36. After the layers formed on the backside surface during forgoing step are removed, a metal layer 60 is then formed, which is used as a bottom electrode 34.
Although the Schottky barrier rectifier disclosed in U.S. Pat. No. 6,404,033 having pluralities of trenches to increase the surface area thereto increases forward current capacity and having buried p layers 30 at the bottom of the trenches to form p-n junction regions to increase breakdown voltage. However, it requires a complex processes at least four to six masks. And also, the buried p-n junctions will introduce many minority carriers when device is under forward bias, which will result in a larger reverse recovery time than the typical Schottky barrier rectifier. The object of the present method is to improve the breakdown voltage and enhance the forward current capacity and simplify the manufacturing processes.